Compositions of thin coatings and their applications as barriers that prevent the temporary functional coatings to interact with the substrate and subsequently acting as rinsable primers to achieve cleaning of the overlying coatings are disclosed. A rinsable primer is defined as a thin material that is applied and cured to a substrate underlying a temporary functional coating, whereby upon removal, the rinsable primer achieves improved cleaning. A temporary functional coating is defined as a material that performs work during a defined single or multi-step manufacturing process, including substrate protection, substrate adhesion (e.g. wafer bonding), mechanical support of the substrate, or the masking of specific areas or patterning (e.g. photoresist). Following the completion of a manufacturing process using a thin cured rinsable primer that is present under a temporary functional coating, a common cleaning process is performed with a cleaner for the temporary functional coating and a rinse/wash for the rinsable primer, followed by a drying step. When utilizing the practice of coating with a rinsable primer and following with a cleaning process, a high degree of cleanliness is achieved.
Proper choice is important of candidate rinsable primers to be used in conjunction with a temporary functional coating. A method of choosing the respective rinsable primer and temporary coating is based upon polarity, or the difference between hydrophilic and hydrophobic character between the rinsable primer and functional coating. The polarity of the surface is estimated by ASTM method D2578, Standard Test Method for Wetting Tension of Polyethylene and Polypropylene Films. The test is based upon the wetting ability of mixed solutions of 2-ethoxyethanol (dielectric constant=29.6) and formamide (polarity=109). For substrates of low surface energy, only those mixtures that are rich in 2-ethoxyethanol will “wet” and spread onto the surface. As formamide content increases, the polarity of the solution increases and if applied to low energy surfaces, it will not spread, but will “bead-up” or reticulate onto the surface and become repelled by the substrate. Therefore, the ASTM method D2578 offers a quick measure of the ability to wet and assess the surface energy of the substrate. The measurement is made in units of dynes/cm2. Material coatings of low surface energy (i.e. <35 dynes/cm2) are classified as more hydrophobic (water hating, repelling), whereas those with properties classified as hydrophilic (water loving, attracting) exhibit higher surface energy (i.e. >55 dynes/cm2). Coatings that widely differ in surface energy are observed to differ in their hydrophilic/phobic and dielectric properties. Surfaces with widely differing character in these areas are expected to act as good choices of rinsable primers and temporary functional coatings for each other.
Once a temporary functional coating has completed its objective, a common cleaning process is performed to remove it and return the substrate to a pristine clean state. Cleaning processes involve direct contact of the cleaning solution to the functional coating, allowing dissolution to occur followed by a rinse and a dry. Electronic substrates must exhibit a high degree of cleanliness in order to allow subsequent manufacturing processes to occur.